The poetic verses contained in the musical compositions written for the Whirling Prayer Ceremony [samâ`, or "sema" in Turkish) have been primarily from Rumi's Divan, and secondarily from poems composed by his son (Sultan Walad, or "Sultan Veled" in Turkish) and his grandson (Ulu `ârif Chelebi). These verses have clearly been specially chosen by the various composer in order to enhance the spirituality of the Whirling Prayer Ceremony and to inspire all the participants in the Ceremony (the semazen's, the leaders of the Ceremony-- such as the shaykh and the chief of the semazen's, and the musicians). The verses consist of quatrains (four lines) or verses of generally one to four lines from ghazals, and are sung by a small chorus.
The musicians who sing the verses are supposed to know the meaning of what they are singing, but knowledge of Persian is rare among the Mevlevis of Turkey. Perhaps there are translations into Turkish of the poems are available for the singers to review. As it is, the verses are sung with thick Turkish accents, so that even native speakers of Persian have difficulty understanding the words.